Generally, automobiles are provided with cooling and heating equipment. The cooling equipment provides a pleasant environment in the vehicle's interior by controlling temperature, humidity and wind speed. An air conditioner represents such a cooling equipment.
An air conditioner consists of three units: a blower, an evaporator and a heater. A blower delivers inside or outside air into the vehicle's interior through a motor. The speed of the motor-driven air delivery can be controlled via three or four graded levels.
The evaporator circulates a coolant, which, after being passed through a compressor, undergoes compression and expansion processes through a belt driven by the engine. This ventilates the air that is cooled by passing through the evaporator into the interior of the vehicle after the air is delivered by the blower.
The heater unit is connected to a coolant line of the vehicle's engine. Thus, the temperature of the coolant increases as the engine becomes heated. Since the coolant is always circulated by a pump, it can be heated while the engine operates, which results in warm air being delivered into the vehicle's interior.
It is common to see a vehicle's cooling device that is provided in a unit structure that emits bad odors inside of the vehicle during the operation of the air conditioner. This occurs because all the air sent by the blower is passed through the evaporator, which is usually wet due to the presence of condensed water—a result of steam from the air condensing due to a drastic change in ambient temperature—thus providing a suitable habitat for fungi and bacteria.
The concentrated water tends to become spattered due to the increased resistance against ventilation, which is a result of the densely arranged radiation fins and an extended volume of ventilation as the vehicle's air conditioner becomes smaller and optimized. Further, when the air is contaminated with foreign materials, such as dust, fungi and bacteria, and passes through the evaporator by being delivered to the inside of a vehicle, it results in the emission of bad odors, which often becomes the cause of respiratory diseases for passengers in the vehicle.
To eliminate bad odors, a compressed aerosol type biocide or a hydrophilic-antimicrobial coating is put on the evaporator. In the case of using a compressed aerosol type biocide, the biocide is sprayed through the exterior inlet and often sticks to the blower or a passage way without reaching the target evaporator. Thus, effective biocidal activity cannot be expected. Further, the masking of bad odors by the sprayed flavors is only temporary and cannot last long. Generally, an aerosol type biocidal and deodorant spray is prepared such that the organic biocide, flavor, and deodorant are mixed with ethyl alcohol and then filled with compressed gas in a container. However, the sprayed biocide cannot reach sufficiently deep into the evaporator to clean it, so the sprayed biocide does not reach the bacteria and fungi to eradicate them.
In the case of applying a hydrophilic-antimicrobial coating on the evaporator, in which the hydrophilic-antimicrobial coating consists of inorganic hydrophilic particles, such as silicates, and an organic binder, the cracks in the coated layer can be easily peeled off when in use because silica particles are relatively large and thus not densely arranged. Further, the coating also provides a frame around the silica particles on which the bad odor-emitting particles as well as bacteria and fungi can grow. The silica particles emits a cement-like smell, which is unpleasant to the driver. In addition, OH− and H+, the hydrophilic groups of the organic hydrophilic antimicrobial binder, react with water, causing the coated layer to decompose and evaporate, thereby exposing the aluminium on the evaporator. In fact, the coated layer lasts up to one or two years after delivery from the factory. These properties can be analyzed via hydrophilic durability test. The initial contact angle is about one to about eight degrees, and the contact angle after durability test is generally above 40 degrees. Therefore, due to the absence of a hydrophilic antimicrobial agent, antimicrobial and bad odors removing properties are accordingly very poor, and the air conditioning function is also deteriorated.